Scanning point source optical energy detector

Abstract

A relatively large field of view is scanned to derive an indication of a point source, optical energy emitter being in the field of view, without recognizing relatively large, non-point emitters in the field of view. Each detector in an array of linearly, arranged point source detectors generates an output current in response to the energy irradiating it. The detectors have slightly displaced, narrow fields of view which are scanned so that the field of view of each detector traces a relatively narrow, substantially straight line path across the large field of view. The paths traced by a pair of detectors are substantially parallel and close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at the outputs of the pair of detectors. Each of a plurality of negative feedback differential operational amplifiers, one for each pair of detectors, includes complementary input and output terminals which are connected to the detectors so that a point source target illuminating one of the detectors is indicated by the polarity of a pulse output of the amplifier. The inputs of the amplifier are connected to spatially arranged detectors in the array so that the large targets are subtracted in the amplifier and are not indicated in the amplifier output. In response to the output signal of each amplifier, an indication is derived to indicate which of the detectors is responsive to a point source.

What is claimed is: 
     
       1. Apparatus for indicating that a point source optical radiation emitter exists in a relatively large field of view, said indication being substantially independent of large, non-point source targets in the field of view, comprising first and second point source detectors for generating output currents in response to said radiation irradiating them, means for scanning the fields of view of the detectors so that the field of view of each detector traces a substantially straight line path across the large field of view, said detectors having slightly displaced fields of view in a direction at right angles to the direction of scan, the spacing of the detectors and the paths traced by the detectors being substantially parallel and close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at outputs of the detectors while images of point sources are indicated as undulations having different wave shapes at substantially the same time positions at outputs of the detectors, a differential amplifier having complementary input terminals and at least one output terminal, said first and second detectors being respectively connected to said complementary input terminals, D.C. negative feedback paths between the input and output terminals, whereby in response to a point source target irradiating one of said detectors there is derived at one of said output terminals a signal including a pulse having a polarity indicative of which of the detectors is irradiated by the point source target, said signal being substantially independent of large targets, and means responsive to the signal for indicating that the pulse is derived from a point source. 
     
     
       2. The apparatus of claim 1 further including a biasing resistor connected between each of the input terminals and a terminal maintained at a D.C. reference potential. 
     
     
       3. The apparatus of claim 2 further including a terminal maintained at a D.C. reference potential in at least one of the feedback paths. 
     
     
       4. The apparatus of claim 1 further including a terminal maintained at a D.C. reference potential in at least one of the feedback paths. 
     
     
       5. Apparatus for indicating that a point source, optical radiation emitter exists in a relatively large field of view, said indication being substantially independent of large, non-point source targets in the field of view, comprising an array of point source detectors for deriving output currents in response to said radiation irradiating them, means for scanning the fields of view of the detectors so that the field of view of each detector traces a substantially straight line path across the large field of view, said detectors having slightly displaced fields of view in a direction at right angles to the direction of scan, the paths traced by the detectors being substantially parallel to each other, a plurality of differential amplifiers, one for each pair of detectors, each of said amplifiers having complementary input terminals respectively responsive to different ones of said detectors, the spacing of the fields of view of the pair of detectors connected to the complementary input terminals of one amplifier being close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at the outputs of the pair of detectors while images of point sources are indicated as undulations having different wave shapes at substantially the same time positions at outputs of the detectors, whereby in response to a point source emitter irradiating one of said detectors there is derived at an output terminal of one of said amplifiers a signal including a pulse having a polarity indicative of which the detectors is irradiated by the point source target, said signal being substantially independent of large targets, and means responsive to the signals derived from the amplifiers for indicating which of the detectors is responsive to a point source. 
     
     
       6. The apparatus of claim 5 wherein said detectors are spatially arranged and connected to the amplifiers so that a point source on a common boundary between the fields of view of a pair of adjacent detectors is indicated as a pulse at an output terminal of at least one amplifier connected to be responsive to the detectors irradiated by the point source on the boundary. 
     
     
       7. The apparatus of claim 6 wherein at least three of said detectors are provided and are linearly aligned in a spatial array, adjacent detectors in the spatial array being connected to input terminals of different ones of said amplifiers. 
     
     
       8. The apparatus of claim 6 wherein N of said detectors are provided, where N is an odd number, and (N+1)/(2) of said amplifiers are provided, one of said detectors feeding two of said amplifiers in parallel. 
     
     
       9. The apparatus of claim 6 wherein N of said detectors are provided, where N is an even number, and (N/2) of said amplifiers are provided. 
     
     
       10. The apparatus of claim 6 wherein adjacent ones of said detectors have their fields of view displaced in the direction of scan so that the adjacent detectors respond at different times to a point source on the boundary, said adjacent detectors being connected to complementary input terminals of one of said differential amplifiers. 
     
     
       11. Apparatus for indicating that a point source optical radiation emitter exists in a relatively large field of view, said indication being substantially independent of large, non-point source targets in the field of view, comprising first and second point source detectors for generating output voltages in response to said radiation irradiating them, means for scanning the fields of view of the detectors so that the field of view of each detector traces a substantially straight line path across the large field of view, said detectors having slightly displaced fields of view in a direction at right angles to the direction of scan, the spacing of the detectors and the paths traced by the detectors being substantially parallel and close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at outputs of the detectors while images of point sources are indicated as undulations having different wave shapes at substantially the same time positions at outputs of the detectors, subtracting means having first and second input terminals and an output terminal at which is derived a signal indicative of the difference between the signals at the first and second input terminals, said first and second detectors being respectively connected to said first and second input terminals, whereby in response to a point source target irradiating one of said detectors there is derived at said output terminal a signal including a pulse having a polarity indicative of which of the detectors is irradiated by the point source targets, and means responsive to the signal for indicating that the pulse is derived from a point source and for indicating which of the detectors is illuminated by a point source emitter. 
     
     
       12. Apparatus for indiating that a point source, optical radiation emitter exists in a relatively large field of view, said indication being substantially independent of large, non-point source targets in the field of view, comprising an array of point source detectors for deriving output voltages in response to said radiation irradiating them, means for scanning the fields of view of the detectors so that the field of view of each detector traces a substantially straight line path across the large field of view, said detectors having slightly displaced fields of view in a direction at right angles to the direction of scan, the paths traced by the detectors being substantially parallel to each other, a plurality of subtracting means, one for each pair of detectors, each of said subtracting means having first and second input terminals respectively responsive to different ones of said detectors, and an output terminal for deriving an output signal indicative of the difference between signals applied by the detectors to the first and second input terminals of the subtracting means, the spacing of the fields of view of the pair of detectors connected to the first and second input terminals of one subtracting means being close enough to each other to enable the images of large targets to be indicated as undulations having approximately the same wave shape at substantially the same time positions at the outputs of the pair of detectors while images of point sources are indicated as undulations having different wave shapes at substantially the same time positions at outputs of the detectors, whereby in response to a point source emitter irradiating one of said detectors there is derived at the output terminal of one of said subtracting means a signal including a pulse having a polarity indicative of which of the detectors is irradiated by the point source target, said signal being substantially independent of large targets, and means responsive to the signals derived from the amplifiers for indicating which of the detectors is responsive to a point source. 
     
     
       13. The apparatus of claim 12 wherein said detectors are spatially arranged and connected to the subtracting means so that a point source on a common boundary between the fields of view of a pair of adjacent detectors is indicated as a pulse at the output terminal of the subtractor means connected to be responsive to the detectors irradiated by the point source on the boundary. 
     
     
       14. The apparatus of claim 13 wherein at least three of said detectors are provided and are linearly aligned in a spatial array, adjacent detectors in the spatial array being connected to input terminals of different ones of said subtracting means. 
     
     
       15. The apparatus of claim 13 wherein adjacent ones of said detectors have their fields of view displaced in the direction of scan so that the adjacent detectors respond at different times to a point source on the boundary, said adjacent detectors being connected to the first and second input terminals of one of said subtracting means.